The present invention relates to a drive unit for crawler working vehicles, which can reduce the fuel consumption.
Hitherto, an aspect of crawler working vehicles is known, which is configured so as to drive left and right traveling parts via a hydrostatically non-stage transmission unit and the speed can be changed in a non-stage while continuing the state in which the traveling power is being transmitted, thereby enhancing the traveling performance for traveling the vehicle on a non-paved road or the like.
Further, another aspect of crawler working vehicles is known, which is so configured as to turn the vehicle body by differing the traveling speeds of the left and right traveling parts from each other by driving the left and right traveling parts each by means of a non-stage transmission unit.
Said conventional crawler working vehicles, however, may suffer from the problems in that performance in traveling in a straight-forward traveling direction may become poor due to an individual difference in left and right non-stage transmission units, irregularity or damages of left and right operation mechanisms for operating the left and right non-stage transmission units or that a farm field surface may be damaged due to a rapid turning resulting from a non-associated control of the left and right non-stage transmission units.
Therefore, proposals have been made that the power from the traveling non-stage transmission units is transmitted to the left and right traveling parts through left and right planetary gear mechanisms and to drive the left and right traveling parts by means of the revolution of the planetary gears of the left and right planetary gear mechanisms by locating a steering non-stage transmission unit for changing the transmission ratio in association with a steering wheel to interlockingly couple the traveling non-stage transmission unit with internally-toothed gears of the left and right planetary gear mechanisms and by interlockingly coupling an output shaft of the steering non-stage transmission unit with left and right sun gears of the left and right planetary gear mechanisms, so as to rotate the left and right sun gears in the directions opposite to each other and further that the vehicle body is turned by differing the traveling speed of the left traveling part from that of the right traveling part by the pivotal operation of the steering wheel.
The conventional crawler working vehicles as described above, however, still have the disadvantages as will be illustrated hereinafter. More specifically, the such conventional crawler working vehicles lack economy in the fuel consumption during traveling on a paved road or the like at a high speed because an efficiency in the power transmission may be decreased rapidly as the number of output revolutions of the hydrostatically non-stage transmission unit becomes larger.
The above-mentioned drive units for the such crawler working vehicles suffer from the disadvantages that a difference in the traveling speeds of the left and right traveling parts is caused to occur regardless of the traveling speed of the vehicle body, so that there is the risk that, on the one hand, the traveling speed of the vehicle body may not be decreased and the vehicle body turns while maintaining its high speed and that, on the other hand, a quick turn may not be made because the vehicle turns while maintaining its low speed during the traveling at a low speed.
The present invention has the object to provide a drive unit for a crawler working vehicle, which can solve the disadvantages and the problems prevailing in the conventional drive units for crawler working vehicles.
The drive unit for a crawler working vehicle in accordance with the present invention, which has an engine interlockingly coupled with left and right sprockets through a traveling non-stage transmission unit and a traveling auxiliary transmission part capable of changing the speed of the vehicle in plural stages, the left and right sprockets being each configured so as to drive the left and right crawlers of the left and right traveling parts.
The drive unit according to the present invention still has the additional features as will be described hereinafter.
(1) The hydrostatically traveling power transmission path is formed between the engine and the left and right sprockets by interlockingly coupling the engine with the input shaft of the traveling non-stage transmission unit, the output shaft of the traveling non-stage transmission unit with the output shaft of the traveling auxiliary transmission part through a traveling clutch, and the output shaft of the traveling auxiliary transmission part with the left and right sprockets. On the other hand, the mechanically traveling power transmission path is formed between the engine and the left and right sprockets by interlockingly coupling the input shaft of the traveling non-stage transmission unit and the traveling auxiliary transmission part with a direct coupling clutch. With this configuration, the drive unit according to the present invention is so adapted as to transmit the traveling power by selecting either one of the hydrostatically traveling power transmission path and the mechanically traveling power transmission path by means of the connection operation or the disconnection operation of each of the clutches.
(2) The drive unit according to the present invention can implement the connection operation or the disconnection operation of each clutch by operating the forward-rearward speed change lever for changing the transmission ratio of the traveling non-stage transmission unit, which in turn is interlockingly coupled with the traveling clutch and the direct coupling clutch.
(3) The drive unit according to the present invention enables the vehicle body to turn in accordance with the output of the steering non-stage transmission unit that in turn is interlockingly coupled in a power transmission path through the left and right planetary gear mechanism, the steering non-stage transmission unit being so adapted as to change the speed in association with the pivotal operation of the steering wheel, and the power transmission path extending from the engine to the input shaft of the traveling part for driving the crawlers of the left and right traveling parts through the traveling non-stage transmission unit. For the drive unit according to the present invention, the left and right steering transmission parts so adapted as to change a speed in plural stages are interposed between the left and right planetary gear mechanisms and the steering non-stage transmission unit, respectively, so that the speed change operation of the left and right steering transmission parts is implemented so as to be associated with the pivotal operation of the steering wheel disposed in the operation part.
(4) The drive unit according to the present invention still has the feature in that the traveling auxiliary transmission part so adapted as to change a speed in plural stages is disposed in the power transmission path extending from the engine to the input shaft of the traveling part for driving the crawlers of the left and right traveling parts through the traveling non-stage transmission unit.
(5) The drive unit according to the present invention still further has the feature in that, when the traveling auxiliary transmission part is operated to change the speed toward a high speed side, the speed change operation of the left and right steering transmission parts is operated so as to be associated with the pivotal operation from the straight-forward traveling status of the steering wheel to decelerate the traveling speed of the traveling part inside the turning than the straight-forward traveling speed of the vehicle body, at least, by decreasing the speed of the steering transmission part inside the turning toward the low speed side. On the other hand, when the traveling auxiliary transmission part is operated to change the speed toward the low speed side, the speed change operation of the left and right steering transmission parts is operated so as to be associated with the pivotal operation from the straight-forward traveling status of the steering wheel to increase the traveling speed of the traveling part outside the turning than the straight-forward traveling speed of the vehicle body, at least, by decreasing the speed of the steering transmission part outside the turning toward the high speed side.